Exchange: Gas Moving molecules
(Mostly O2)
BSCI 207: Organismal Biology
Organismal perspective
Form and function
Design principles
Evolutionary survey
Physics and phylogeny
BSCI 105 / BSCI 106
or AP Biology course
www.vashonsd.wednet.edu/everest/itinerary.htm
Each Fundamental Process of Life
Universal physical
and chemical
principles
Diversity of Life
places design
constraints on
provides certain
opportunities for
and/or
Common genomic
toolkit from LUCAC
Ecological roles
Organismal
strategies
provides molecular
solutions for
can evolve for
Different cells,
tissues, & organs
selection pressures
Unity of Life
1. Big Steps in the Origin of Life
Origin of information processing/replication system
Origin of metabolism for generating small organic
molecules and larger polymers
Origin of bioenergetics
Origin of lipid membranes defining the boundary of
life the challenge of impermeable membranes
C & R 26.12
2. Difference between Gas Exchange and
Nutrient Assimilation - F. Fig. 6.8
Gases - high permeability -> do not require transport proteins
Nutrients - low permeability -> require selective transport proteins
3. Learning objectives - Unique gas exchange
and circulatory systems in multicellular lineages
1. No specializations for gas exchange and circulation in
unicellular organisms - passive diffusion only
2. Independent origins of gas exchange and/or circulatory
systems in various multicellular animal and plant
lineages
3. Physical constraints (Ficks Law and Hagen-Poiseuille
equation) operating on convergent structures
Introduction - Diffusion in cells
Diffusion works fine across membranes, organelles, and most cells
In general, no need to evolve special mechanisms for facilitating
the movement of most molecules via diffusion over short distances.
(Exception: the challenge of membrane permeability for most
large, charged, and/or polar molecules)
Introduction - Ventilatory and
circulatory systems in animals
more in later lectures!
F Fig. 44.11
arditobook.pbworks.com/The-Circulatory-System
Ventilation
Circulation
Bulk flow/convection of medium (air) Bulk flow/convection of medium (blood)
Diffusion of O2 and CO2 across
Diffusion of gases, food molecules, and
alveolar membranes
waste products across capillary
membranes
Gas exchange Unity of Life
Ficks Law
Common physics expression
Flux = per unit area of an organ
Alternative biological expression
Flow = total capacity of an organ
Gas exchange
Fick Equation incorrect
bio textbook version
Flow is R rate of gas exchange
R is proportional to A organ surface area
Pp partial pressure
(proportional to gas conc.)
R is inversely proportional to x thickness (dont use D)
Diffusion coefficient D (dont use k) depends on the
molecular and the medium
Acceptable bio version:
Gas exchange organs
Useful properties
The Fick Equation
Rate or Flow = -D*A* (pp/x). Want to maximize Rate
Cant do much about D - depends on the diffusing molecule
and the medium (air vs. water!!!!!!)
A - Large area
high flow
Pp Large difference in partial pressure
high flow
x - Thin boundary
high flow
Gas exchange organs large area but often fragile;
Design constraints/functional conflicts???
Gas exchange - Diversity of Life
Most important axes of diversity are:
Phylogeny
Size (scaling principles)
Metabolic Rate
Medium
Gas Exchange
Unicellular organisms
Favorable scaling relationships
Large surface/volume
Short diffusion distances
Unfavorable relationships
Viscosity of water slow rate of bulk
flow
Low concentration of O2 in water
Simple diffusion sufficient
Gas Exchange - Terrestrial Plants
Life on land is really tough
Face a problem. Must
conserve water
Waxy cuticle
Regulate temperature
Release O2
Avoid photorespiration
(burns up the Calvin
Cycle intermediates)
Acquire CO2
Photosynthesis
C&R 36.10
Gas Exchange - Terrestrial Plants
Face a major conflict of physiological processes
A difficult tradeoff, made worse by very unfavorable
gradients!
pp CO2 low in atmosphere (0.035%) - small inward gradient
pp H2O often low in atmosphere - large outward gradient
Transpiration (evaporation) to photosynthesis ratio
Ratio of H2O out gradient/CO2 in gradient
Varies, but often about 600!
Large oak tree can transpire 150,000 liters = 40,000 gallons
per year
Gas Exchange - Terrestrial Plants
Leaf Structure
Cuticle - prevent
uncontrolled water loss
Stomata - allow and regulate
gas exchange
Interior of leaf filled with
spaces
Diffusion distances short
(within leaf)
High internal surface area
for gas exchange
C&R Exchange 35.19c
Gas - Terrestrial Plants
Leaf Structure
Fig. 35.17
No gas exchange organ
Numerous microscopic stomates exchange
gases across epidermal surfaces of leaves
Each stomate is surrounded by a pair of
expandable guard cells
Fig. 35.25
Gas Exchange Stomatal action
1-2% of surface area, account for 90% of water loss
Guard cells
In pairs
Turgid -> Open
Flaccid -> Closed
Ideas for how this is
accomplished?
Gas Exchange
1-2% of surface area, account
for 90% of water loss
Guard cells
In pairs
Turgid -> Open
Flaccid -> Closed
Controlled by flux
of K+ in guard cells
Utilizes H + electrochemical gradient
Water follows K +, affecting turgidity
Fig. 39.12
MORE TO COME!
Gas Exchange in Animals
Porifera, Cnidaria, Platyhelminthes
Diffusion distances
short
Full of holes - Porifera
Septate - Cnidaria
Flat - Platyhelminthes
Diffusion fine for
uptake and distribution
No specialized gas
exchange or circulatory
organs
Gas Exchange in Animals
Porifera, Cnidaria, Platyhelminthes
Sufficiency and constraints of Diffusion
Todd (and Albert) sez:
Example: Flatworm
Einsteins solution to t = x2/2D
Ficks 2nd Law:
x=(2Dt)1/2
Biological variation:
Maximum
thickness = (2Dpp/m)1/2
pp = difference, m = metabolic rate (O2/g/hr)
Given the metabolic rate of a flatworm, D for O2 in tissue,
and the gradient, you can calculate how flat the worm
needs to be!
Gas Exchange in Animals
Porifera, Cnidaria, Platyhelminthes
Given the metabolic rate of a flatworm, the diffusion
coefficient of O2 in tissue, and typical values of pp:
(2Dpp/m)1/2 = 0.5 mm
Gas Exchange in Animals
Aquatic Invertebrates
Highly variable, depending on
Habitat
Activity level
Feeding mode
Etc.
Respiratory structures
Skin
Surface elaborations
Highly organized gills
Complex respiratory organs
several independent origins
More later (vertebrates)
C&R 42.19
Gas Exchange in Animals
Aquatic Invertebrates
Highly variable, depending on
Habitat
Activity level
Feeding mode
Etc.
Respiratory structures
Skin
Surface elaborations
Highly organized gills
Complex respiratory organs
several independent origins
coupled to circulatory systems
More later (vertebrates))
Gas Exchange in Animals
Terrestrial Invertebrates
Gills generally not suitable for gas exchange in air
Collapse due to gravity and surface tension
Occasionally modified for use in air
Lungs
Respiratory organs of
land animals several
independent origins
Internal supports, various
elaborations
Coupled to circulatory sys.
More later (vertebrates)
Gas Exchange in Animals
Terrestrial Invertebrates
Gills generally not suitable for gas exchange in air
Collapse due to gravity and surface tension
Occasionally modified for use in air
Lungs
Variously elaborated
More later
(vertebrates)
Tracheal systems
Insects
Convergently
elsewhere
Gas Exchange in Animals
Terrestrial Invertebrates
Tracheal systems
Ramify throughout body
Tracheal opening (spiracle)
can be regulated
Diffusion distances short
Sufficient for small insects,
if not very active
Diffusion easy in air
(more later)
Why could insects this large
never exist?
A number of reasons, actually
2) Diffusion - the problem
SMALL INSECT
LARGE INSECT
Oxygen depleted if tube
diameter stays the same
Tracheole volume larger
to accommodate needs
Gas Exchange in Animals
Terrestrial Invertebrates
Tracheal systems
Ramify throughout body
Tracheal opening (spiracle) can be regulated
Diffusion distances short
Larger, more active
insects supplement
diffusion with bulk flow/
circulation/convection
Body compression
Movement of internal
fluids
http://insects.tamu.edu/
Gas Exchange in Animals
Terrestrial Invertebrates
Tracheal systems
Ramify throughout body
Tracheal opening (spiracle) can be regulated
Diffusion distances short
Larger, more active
insects supplement
diffusion with bulk flow
Body compression
Movement of internal
fluids
http://insects.tamu.edu/
Gas Exchange in Animals
Terrestrial Invertebrates
Tracheal systems
Ramify throughout body
Tracheal opening (spiracle) can be regulated
Diffusion distances short
Larger, more active
insects supplement
diffusion with bulk flow
Body compression
Movement of
internal fluids
Fig. 44.7
A parting question
In the Paleozoic Era (> 300 mya), there lived
terrestrial arthropods more than 10x the size of their
modern counterparts! Dragon flies with wingspans of
0.8 meters! How could that be?
Assuming that they relied
on diffusion (i.e., no active
pumping), then how?
Think about the variables
of Ficks Law: